Bulk bags are used for the transportation of bulk loose materials. Bulk bags are usually fabricated by stitching or sewing pieces of woven fabric into various shapes, including a tubular shape. A conventional bulk bag has a lifting mechanism in the form of lift straps or lifting stevedores sewn onto the body fabric so that the bulk bag can be lifted by a forklift or other lifting machinery using the lifting mechanism of the bulk bag. A conventional bulk bag has square or rectangular walls which can be made with various way, such as U-panel, circular, 4-panel, etc.
Prior art bulk bags have various issues with the shape of the bag after filling. Due to the flexible nature of the body fabric, after the bag is filled, the sides of the bags will naturally round out or bulge out from the original square or rectangular shape. Since the top and bottom pieces of the bag is usually square or rectangular, the bulging-out is more severe where it is farther away from the top and bottom of the bag. The most severe part of the bulging is about the middle portion along the vertical direction of the walls. Due to the gravity of the content in the bag, the most severe location is usually slightly lower than the very middle point of the wall.
It has been a significant problem when a bulk bag bulges out. When the bag is loaded into a truck or ocean shipping container, the bag footprint size has to be significantly reduced so the bags can fit into the space. This leaves valuable space unfilled in the truck. The shipping costs per unit is increased due to this waste.
During bag handling, bulging-out portion of the bag usually over-hang outside of the pallet. This significantly increases the chance of bag damage since the over-hanging portion can rub against the truck wall, another bag, the neighboring pallet or the filling/handing machinery.
Another impact of the bulging is the bag stability. The bulging-out portion is outside of the footprint of the bag. This can render the bag into an unstable state especially when the bag is taller, being moved, or placed on an uneven surface.
Over the short history of bulk bags, very significant efforts have been spent to develop all different types of baffled bags to solve the bulging problem. A baffle is normally a piece of fabric or threads placed inside of the bag, connecting the neighboring or opposite walls of the bag from inside so the walls can be held in position when the bag is filled. If inside of a liner, baffles made of materials similar to the liner, can be used in the similar fashion to achieve the similar result. Other than the baffled bags, there has been no other successful ways developed to solve the bulging problem on a bulk bag.
Baffled bags are successful in reducing the bulging of the bag. Some bulging still exists on baffled bags on the wall fabric between the baffle connecting points. The major problem with baffled bags is apparently the much higher cost. More material is needed to make the bag and the manufacturing process is much slower. The presence of a baffle also increases the chance of contamination to the content of the bag.
There have been barely any other successes in reducing the bag bulging other than the usage of baffles. There is one work where the top edge of the bag is reduced hopefully the keep the body vertically straight but it does not improve the bulging which is caused by the natural round out of the body.